Navigation device and navigation method

ABSTRACT

The present invention is to provide a navigation device having a function of starting a route re-searching early by predicting a route change of a vehicle from a recommended route. A navigation device is formed such that when guiding a vehicle by virtue of a recommended approaching route and a recommended exit route both connected to a branching point, and once the vehicle traveling from the recommended approaching route and heading for the branching point is about to deviate from the recommended exit route, said navigation device starts a route re-searching for finding a new recommended route going through other route. The navigation device detects that a turning angle θx of the vehicle is about to be in a direction within an angle range not including an angle formed between the direction θa of the recommended approaching route and the direction θb of the recommended exit route, and starts a route re-searching to find a new recommended route going through other route existing within an angle range excluding an angle formed between the directions θa and θb.

TECHNICAL FIELD

The present invention relates to a navigation device having a routere-searching function, and to a navigation method.

BACKGROUND ART

A traditional vehicle navigation device has a route re-searchingfunction (automatic re-routing function), so formed that when thevehicle is guided by searching a recommended route to a destinationspecified by a user and then out of the recommended route to change theroute, the re-searching function automatically starts a re-searching tofind a new recommended route so as to guide the vehicle to a destinationthrough a changed route (see patent documents 1 and 2).

In patent document 1, when the navigation device detects a change of theroute of the vehicle from the recommended route, a new recommended routeis searched again and stored in a storage device. When a user instructsto start the route re-searching, a new recommended route stored in thestorage device is displayed so as to guide a vehicle.

In patent document 2, when a vehicle traveling on a recommended routechanges a lane before a branching point (for example, an intersection)and then travels for a specified time or longer on the changed lane, itwill be determined that the vehicle is going to change its route fromthe recommended route, and the route re-searching is thus started. Afterthe route change from the recommended route is confirmed, the newrecommended route is displayed to guide the vehicle.

With regard to the route re-searching function disclosed in patentdocument 2, when a turning signal of the vehicle has been detectedbefore the branching point for a specified time or longer, the routere-searching function will determine that the vehicle is going to turnright or left to change its route from the recommended route, therebystarting the route re-searching. After confirming that a route has beenchanged from the recommended route, the device may display a newrecommended route searched beforehand, so as to guide the vehicle.

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. H09-152352

Patent Document 2: Japanese Unexamined Patent Application PublicationNo. 2004-61356

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

As shown in a time chart of FIG. 1( a), after confirming that thevehicle has changed its route from the recommended one, the navigationdevice of patent document 1 will start a route re-searching, and preparea new recommended route in a time period before the user instructs tostart the route re-searching. However, the old recommended route willcontinue to be displayed until the user instructs to start the routere-searching and a new recommended route will not be displayed until theuser recognizes the old recommended route himself and instructs tore-search a route, thus causing an inconvenience to the user.

The navigation device of patent document 2, as shown in a time chart ofFIG. 1( b), detects a lane change or a turn signal of a vehicle and thenstarts a route re-searching before confirming a route change of thevehicle from a recommended one. Then, after confirming that the vehiclehas changed its route from the recommended one, a re-searched newrecommended route is displayed so to effect a seamless guidance.

However, in patent document 2, the function of starting a routere-searching depends on a road with a lane changing path on it. On aroad without such a lane changing path, it will be difficult todetermine whether a vehicle is about to change its route from arecommended one, thus making it difficult to perform an effective routere-searching.

Moreover, though a route re-searching is started upon detecting aturning signal, since the turn signal is dealt only inside the directionindicator of the vehicle, such a turn signal is not output to otherelectric devices such as a navigation device. Therefore, it isimpossible for the navigation device to start a route re-searching basedon the turn signal.

The present invention is provided to solve the above-mentioned problems.An object of the present invention is to provide a navigation device anda navigation method, with the navigation device having a novel functionof starting a route re-searching early by predicting a route change of avehicle from a recommended route.

Means of Solving the Problems

An invention recited in claim 1 is a navigation device formed such thatwhen guiding a vehicle by virtue of a recommended approaching route anda recommended exit route both connected to a branching point, and oncethe vehicle traveling from the recommended approaching route and headingfor the branching point is about to deviate from the recommended exitroute, the navigation device starts a route re-searching for finding anew recommended route going through other route. This navigation devicecomprises route change determination device for detecting that a turningangle of the vehicle is about to be in a direction within an angle rangenot including an angle formed between the direction of the recommendedapproaching route and the direction of the recommended exit route,thereby starting the route re-searching.

An invention recited in claim 2 is also a navigation device formed suchthat when guiding a vehicle by virtue of a recommended approaching routeand a recommended exit route both connected to a branching point, andonce the vehicle traveling from the recommended approaching route andheading for the branching point is about to deviate from the recommendedexit route, the navigation device starts a route re-searching forfinding a new recommended route going through other route. Thisnavigation device comprises route change determination device fordetecting that a turning angle of the vehicle is within an angle rangenot including a predetermined threshold angle range having the directionof the recommended approaching route as a reference, is about to be in adirection exceeding a direction of the recommended exit route from adirection of the recommended approaching route, or a direction oppositeto the direction of the recommended exit route, thereby starting theroute re-searching.

An invention recited in claim 5 is also a navigation device formed suchthat when guiding a vehicle by virtue of a recommended approaching routeand a recommended exit route both connected to a branching point, andonce the vehicle traveling from the recommended approaching route andheading for the branching point is about to deviate from the recommendedexit route, the navigation device starts a route re-searching forfinding a new recommended route going through other route. Thisnavigation device comprises route change determination device whichcompares an actual distance extending from the branching point to avehicle position, with a required distance extending from the branchingpoint to the vehicle position, the required distance being necessary forthe vehicle to enter the branching point at a speed of the vehicletraveling on the recommended approaching route and move to therecommended exit route through the branching point. When the actualdistance is shorter than the required distance, the navigation devicestarts the route re-searching.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides explanatory views for explaining route re-searchingfunctions of a conventional navigation device.

FIG. 2( a) is a bock diagram showing a constitution of a navigationdevice of a preferred embodiment, FIG. 2( b) is an explanatory viewexplaining entities of road data.

FIG. 3 is a flow chart explaining functions and operations of thenavigation device shown in FIG. 2( a).

FIG. 4 provides explanatory views explaining the functions andoperations of the navigation device shown in FIG. 2( a).

FIG. 5 provides explanatory views further explaining the functions ofthe navigation device of the preferred embodiment.

FIG. 6 is a flow chart explaining functions and operations of thenavigation device formed according to a first embodiment.

FIG. 7 provides explanatory views further explaining the functions ofthe navigation device of the first embodiment.

FIG. 8( a) is a block diagram showing the constitution of a navigationdevice formed according to a second embodiment, FIGS. 8(b) to 8(e) areexplanatory views schematically explaining functions.

FIG. 9 is a flow chart explaining functions and operations of thenavigation device of the second embodiment.

FIG. 10 is an explanatory graph showing the functions of the navigationdevice of the second embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

A preferred embodiment of the present invention will be set forth indetail with reference to FIGS. 2 through 5. First, entities of road dataused in a route searching and a route re-searching by the navigationdevice of the present embodiment will be explained using FIG. 2( b).

The road data comprise: as main entities (basic data factors), linksconnected by state changing points where the shape or direction of roadin a map changes, and by a branching points (such as intersections); andnodes indicating coordinates of both ends of each link. At each statechanging point, two links are connected by the same node. At eachbranching point (for example, an intersection), three or more links areconnected by the same node. Roads are expressed by the coordinate rowsof connected links. Therefore, a state changing point is a nodeconnecting two links, while a branching point is a node connecting threeor more links.

In the present embodiment, the navigation device finds a recommendedroute to guide a vehicle to a destination using the road data stored ina storage unit 3 shown in FIG. 2( a).

As shown in FIG. 2( a), the navigation device 1 of the presentembodiment comprises: a vehicle position detection unit 2, a storageunit 3, a display unit 4, an operation unit 5, and a control unit 6. Thecontrol unit 6 comprises: a map matching unit 7, a recommended routesearching unit 8, and a route change determination unit 9.

The vehicle position detection unit 2 detects a vehicle position or thelike by combining GPS (Global Positioning System) navigation with aself-support navigation, while a detection result is supplied to thecontrol unit 6. Namely, the vehicle is positioned by the GPS navigationmethod using GPS and surveyed based on a turning angle θx of thevehicle, a vehicle speed Vx or the like, all measured by censors such asa gyro censer and a speed censor. Then, the vehicle positions measuredby the GPS navigation and the self-support navigation are combined toperform a predetermined supplementary processing. In this way, a moreaccurate vehicle position Ps can be detected to provide the control unit6 with detected data regarding the behavior of the vehicle (thereafter,referred to as “the behavior data”) such as vehicle position Ps, aturning angle θx, and a vehicle speed Vx.

The storage unit 3 includes a database storing spatiotemporal data (SI:Spatial Information) such as the above-mentioned road data and map data,and serves as an operating area for the control unit 6, the map matchingunit 7, the recommended route searching unit 8, and the route changedetermination unit 9 in performing the below-described processing.

The display unit 4 displays not only a map image based on the map datastored in the storage unit 3, but also a recommended route searched orre-searched by the recommended route searching unit 8 and a vehicleposition Px processed by the map matching unit 7 in accordance with theroad on the map image, thereby guiding a vehicle to a destination.

The operation unit 5 is provided for a user to give instruction forfinding a route extending from the present position to a desired(specified) destination.

The control unit 6 has a micro processor (MPU) and a digital signalprocessor (DSP) which intensively control the operation of thenavigation device 1. The map matching unit 7, the recommended routesearching unit 8 and the route change determination unit 9 are realizedby executing specified programs by MPU and DSP. Namely, the map matchingunit 7, the recommended route searching unit 8, and the route changedetermination unit 9 are software.

The map matching unit 7 converts the behavior data such as the vehicleposition Ps, the turning angle θx, and the vehicle speed Vx detected bythe vehicle position detection unit 2 into a traveling path (such as thepresent position of the vehicle, the direction of the travelingvehicle). By finding the road data in the specified range (area) on themap including the traveling path as proposed data from the road datastored in the storage unit 3 and by comparing a driving path to nodesand links of the recommended road data, the most recommendable road dataincluding nodes and links suitable for the traveling path is determined.Then, the vehicle position Ps is moved (for correction) to the node andlink sides of the most recommendable road data, so as to be adjusted tothe road on the map. The adjusted vehicle position Px is displayed inthe display unit 4.

In other words, the map matching unit 7 converts the vehicle position Psdetected by the vehicle position detection unit 1 into the vehicleposition Px adjusted to the road on the map image, so as to prevent thevehicle from being displayed out of the map image.

When a desired destination is input by a user through the operation unit5, the recommended route searching unit 8 finds a recommended route fromthe present vehicle position (vehicle position Px processed in theabove-mentioned map matching) to the destination using the road datastored in the storage unit 3, and displays the recommended route in thedisplay unit 4. The recommended route searching unit 8 automaticallystarts the route searching which is the same as the previous routesearching, based on the result of the route change determinationprovided by the route change determination unit 9. The new recommendedroute to the destination, obtained by route re-searching, is displayedin the display unit 4.

The route change determination unit 9 operates to determine whether thevehicle traveling along the recommended route is about to change itsroute to other route than the recommended route at the branching pointG. According to the result of the route change determination, the routechange determination unit 9 causes the recommended route searching unit8 to starts a route re-searching. The details of functions of the routechange determination unit 9 will be explained with reference to a flowchart shown in FIG. 3.

The functions and operations of the navigation device 1 will beexplained with reference to the flow chart of FIG. 3 and diagrams ofFIGS. 4( a) and (b). However, the following explanation will mainlydescribe the functions and operations of the navigation device 1 under acondition where the vehicle traveling along the recommended routesearched or re-searched by the recommended route searching unit 8deviates from the recommended route to other route at the branchingpoint G.

FIG. 3 is a flow chart showing the processing of the route changedetermination unit 9. What are input to the route change determinationunit 9 are the recommended route data found by the recommended routesearching unit 8, the turning angle θx detected by the vehicle positiondetection unit 2, and the vehicle position Px generated by the mapmatching unit 7.

At step ST1, the route change determination unit 9 compares the vehicleposition Px with the recommended route and determines whether thevehicle is approaching the branching point G. By comparing the vehicleposition Px to nodes and links serving as important factors of therecommended route, it is determined whether the vehicle has entered anarea separated at a predetermined distance from the node of thebranching point G positioned before the vehicle position Px (thereafter,“branching area”), with nodes of state changing points being excludedand nodes of branching points serving as determination objects.

As shown in FIG. 2( b), since the node of each state changing pointconnects two links rather than three or more links, they are excludedfrom determination objects as nodes not having any possibility of routechanging, while a node connecting more than three links will bedetermined to be the node having the possibility of route changing, andthus deemed as determination object.

When the recommended routes A and B are displayed as a dot line on themap image of the display unit 4 as schematically shown in FIG. 4( a), orwhen the recommended routes A and B are displayed as a dot line in thedisplay unit 4 as schematically shown in FIG. 4( b), if a vehicletraveling along the recommended route A enters the branching area of thebranching point G, the vehicle will be determined to be approaching thebranching point G (step ST1: “yes”).

Even though a recommended route to the branching area G has many curvesdue to the excluding of the nodes of the state changing points from thedetermination objects, the vehicle is determined to be traveling on aroad along the recommended route and determined to be “No” until thevehicle enters the branching area.

Branching areas are calculated with each containing one branching pointG and set within a range shorter than a vehicle traveling link connectedto the node of the branching point G (for example, in FIGS. 4( a) and(b), a link of the recommended route A connected to the branching pointG), but larger than the branching point G (area of the intersectionobtained from the map data). Namely, by setting the branching area to atleast the area of the branching point G, it is possible to highlyaccurately determine that the vehicle has approached the branching pointG.

FIG. 4( a) shows a pattern that the recommended route B ahead of thebranching point G (thereafter, “recommended exit route”) is to the rightside of a recommended route on which the vehicle approaches thebranching point G (thereafter, “recommended approaching route”). FIG. 4(b) shows a pattern that the recommended exit route B is to the left sideof the recommended route A.

Once the route change determination unit 9 determines, in theabove-mentioned step ST1, that the vehicle is approaching the branchingpoint G, the process proceeds to step ST2 where the direction θa of therecommended approaching route A and the direction θb of the recommendedexit route are detected based on the respective links. In FIG. 4( a),the direction θb of the recommended exit route B to the right side ofthe recommended approach route A is detected. In FIG. 4( b), thedirection θb of the recommended exit route B to the left side of thedirection θa of the recommended approaching route A is detected.

At step ST3, the route change determination unit 9 takes the directionGb of the recommended exit route B as a standard direction, sets anarrow angle range (180° and under) from the direction θb of therecommended exit route B to 180° as a first angle range W1, and anotherangle range (an angle range of 180°) from the direction of θa to 180°excluding the direction θb of the recommended exit route B as a secondangle range W2.

Namely, in FIG. 4( a) the first angle range W1 is set as the range fromthe direction 9 b of the recommended exit route B pointing to the rightof the direction θa of the recommended approaching route A, clockwise tothe direction θr (180°). Meanwhile, the second angle range W2 is set asthe angle range from the direction θa of the recommended approachingroute A counterclockwise to the direction θr.

In FIG. 4( b), the first angle range W1 is set as the range from thedirection θb of the recommended exit route B pointing to the left of thedirection θa of the recommended approaching route A, counterclockwise tothe direction θr (180°). Meanwhile, the second angle range W2 is set asthe angle range from the direction θa of the recommended approachingroute A clockwise to the direction θr.

At step ST4, the route change determination unit 9 determines whetherthe turning angle θx has exceeded the direction (θb+THD) in the firstangle range W1. Here, the direction THD is the minimum angle (athreshold value) capable of detecting the turning angle of the vehicle.

Then, as shown in FIG. 4( a), when the turning angle θx becomes thedirection θxb and the direction θxb has developed from the direction θaand clockwise exceeded the direction (θb+THD), the turning angle isdetermined “exceeded”.

As shown in FIG. 4( b), when the turning angle θx becomes the directionθxb and the direction θxb has developed from the direction θa andcounterclockwise exceeded the direction (θb+THD), the turning angle isdetermined “exceeded”.

Namely, at step ST4, it is determined whether the vehicle has turnedtowards the recommended exit route B and the direction θx has become thedirection θxb exceeding the direction (θb+THD). When the turning angleθx is determined to be exceeding the direction (θb+THD) in the firstangle range W1 (“yes”), the process proceeds to step ST10 where it isdetermined that there is an omen of vehicle's changing its route fromthe recommended route. On the other hand, if it is determined that theturning angle has not exceeded the aforementioned angle (“No”), theprocess proceeds to step ST5.

At step ST5, the route change determination unit 9 determines whetherthe turning angle θx of the vehicle has exceeded the direction (θa+THD)in the second angle range W2. Then, as shown in FIG. 4( a), when theturning angle θx has become the direction θxa which has developed fromthe direction θa and exceeded counterclockwise the direction (θa+THD),the turning angle is determined “exceeded”.

As shown in FIG. 4( b), the turning angle θx becomes a direction θxa.When the direction θxa has clockwise exceeded the direction (θa+THD)from the direction θa, the turning angle is determined “exceeded”.

At step ST5, it is determined whether the vehicle has turned to theopposite direction of the recommended exit route B. When the turningangle θx is determined to have exceeded the direction (θa+THD) in thesecond angle range W2 (“Yes”), the process proceeds to step ST20 whereit is determined that the vehicle has an omen of deviating from therecommended route so as to change its route. On the other hand, if it isdetermined that the angle θx has not exceeded the direction (θa+THD)(“No”), the process proceeds to step ST6.

At step ST6, the route change determination unit 9 compares the vehicleposition Px with the coordinate of the node of the branching point G,then determines whether the vehicle has passed through the branchingpoint G. When the vehicle is determined to have passed through thebranching point G (“yes”), the process proceeds to step ST30. If not(“No”), the process proceeds to step ST4.

Next, description is given to explain an operation which is performedwhen at step ST10 the route change determination unit 9 has determinedan omen of changing route. Namely, at first, at step 10 the route changedetermination unit 9 provides the recommended route searching unit 8with the result of the route change determination. Next, at step ST11,the object angle range WD1 is set to cover an angle range from thepresent turning angle θx to the direction θr in the first angle rangeW1. Other routes in the object angle range WD1 are searched in the roaddata stored in the storage unit 3.

For example, as shown in FIG. 4( a), when the vehicle turns right andthere is only one other route R1 in the object angle range WD1developing from the turning angle θxb to the direction θr, such an otherroute R1 is searched. If there are several other routes, these severalother routes are searched. On the other hand, if there are no otherroutes, the searching is finished and the process proceeds to step ST12.

On the other hand, as shown in FIG. 4( b), when the vehicle turns leftand there is one other route L1 in the object angle range WD1 developingfrom the turning angle θxb to the direction θr, such an other route L1is searched. If there are several other routes, these several otherroutes are searched. On the other hand, if there are no other routes,the searching is finished and the process proceeds to step ST12.

At step ST12, the route change determination unit 9, using the result ofthe above-mentioned searching, determines whether other route is onlyone. If yes, the process proceeds to step ST13. If other routes areseveral or none (“No”), the process proceeds to ST30.

Namely, as shown in FIGS. 4( a) and (b), when the vehicle turns right orleft and there is only one other route R1 or L1 in the object anglerange WD1, the process proceeds to step ST13.

At step ST13, the recommended route searching unit 8 starts the routere-searching to find a new recommended route to guide a vehicle to adestination by going through the above-mentioned single other route,based on the result of the route change determination performed by theroute change determination unit 9. In other words, in FIG. 4( a), theroute re-searching is started to find a new recommended route goingthrough other route R1. In FIG. 4( b) the route re-searching is startedto find a new recommended route L1 going through other route L1.

Next, at step ST14, the control unit 6 compares the vehicle position Pxto the node of the branching point G to determine whether the routechange through the branching point G to other route has been decided. Ifthe route change has been decided, the process proceeds to step ST15,and a new recommended route re-searched by starting the re-searchingperformed by the recommended route searching unit 8 is updated anddisplayed on the display unit 4. Then, the process returns to step ST1to repeat the previous processing.

In this way, after processing at steps ST10 through ST15, before thevehicle goes through the branching point G, the route re-searching isstarted predicting that the route will be changed to other routeexisting on the side of the direction θb of the recommended exit route B(in the object angle range WD1). Hence, when the route change isdecided, the new recommended route can be promptly displayed so as toguide the vehicle.

Next, description is given to explain a condition where at step ST20 theroute change determination unit 9 has determined an omen of changingroute. Namely, at first, at step 20 the route change determination unit9 provides the recommended route searching unit with the result of theroute change determination. Next, at step ST21, the object angle rangeWD2 is set to cover an angle range from the present turning angle θx tothe direction θr in the second angle range W2. Other routes in theobject angle range WD2 are searched in the road data stored in thestorage unit 3.

For example, as shown in FIG. 4( a), when the vehicle turns to the leftof the direction θa of the recommended approaching route A and there areother routes L2 and L1 in the object angle range WD2 developing from theturning angle θxa to the direction θr, the other routes L2 and L1 aresearched. However, when no other routes are found, the searching isfinished, and the process proceeds to step ST12.

Further, as shown in FIG. 4( b), when the vehicle turns to the right ofthe direction θa of the recommended approaching route A and there areother routes R2 and R1 in the object angle range WD2 developing from theturning angle θxa to the direction θr, the other routes R2 and R1 aresearched. However, when no other routes are found, the searching isfinished, and the process proceeds to step ST12.

At step ST12, it is determined whether there is only one other route,and if there is only one (“Yes”), the process proceeds to step ST13.When there are several other routes or no other route (“No”), theprocess proceeds to step ST30.

As shown in FIGS. 4( a) and (b), when there are several other routes L1and L2 or R1 and R2 in the object angle range WD2, the process proceedsto step ST30. On the other hand, even if there are no other routes, theprocess also proceeds to step ST30. Further, If there is only one otherroute L1 or R1 in the object angle range WD2, the process proceeds tostep ST13.

At step ST13, the recommended route searching unit 8 starts routesearching to find a new recommended route so as to guide the vehicle tothe destination through the above-mentioned single other route, inaccordance with the result of the route change determination sent fromthe route change determination unit 9. At step ST14, the control unit 6determines whether the vehicle has passed through the branching point Gand decided to change its route to other route. When the route changehas been decided, the process proceeds to step ST15, and the newrecommended route re-searched by the recommended route searching unit 8is updated and displayed on the display unit 4. Subsequently, theprocess proceeds to step ST1 to repeat its previous steps.

In this way, when steps, ST20, ST21, and ST12 though ST15 are executedand the vehicle has not passed through the branching point G, predictionis performed to predict an omen in which the vehicle might change toother route existing on an opposite side away from the direction θb ofthe recommended exit route B (in the object angle range WD2), followedby starting a route re-searching. As a result, it is possible to showthe user a new recommended route and guide the vehicle soon after theroute change has been decided.

As mentioned above, when the route change determination unit 9determines at step ST6 that the vehicle has passed through the branchingpoint G, the process proceeds to step ST30. When it is determined atstep ST12 that there are several other routes, the process proceeds tostep ST30. At step ST30 the control unit 6 determines whether thevehicle has passed through the branching point G and has decided tochange to other route. When the route change is decided, the controlunit 6 causes the recommended route searching unit 8 to start the routere-searching. Namely, at step ST30, the route re-searching is started tofind the new recommended route going through other route not when theroute changing of the vehicle is predicted, but when the route changinghas been decided. Then, at step ST15, the new recommended route isupdated and displayed in the display unit 4. Subsequently, the processreturns to step ST1 to repeat its previous steps.

As explained above, according to the navigation device 1 of the presentembodiment, when the vehicle goes into the branching area of thebranching point G, the direction θr is set to 180° opposite to thedirection θa of the recommended approaching route A; the first anglerange W1 is set to the angle range from the direction θb of therecommended exit route to the direction θr; the second angle range W2 isset to the angle range from the direction θa of the recommendedapproaching route A to the direction θr excluding the direction θb ofthe recommended exit route B. When the turning angle of the vehicle θxhas exceeded the direction θb in the first angle range W1, or theturning angle θx of the vehicle has exceeded the direction θa in thesecond angle range W2, the route re-searching is started expecting thatthe vehicle will deviate from its recommended route. Hence, the routere-searching can be promptly started before the vehicle goes through thebranching point G.

Namely, in the navigation device 1 of the present embodiment, when theturning angle θx is detected to be in the direction of an angle rageexcluding an angle range between the direction θa of the recommendedapproaching route A and the direction θb of the recommended exit routeB, the route re-searching can be restarted promptly before the vehiclegoes through the branching point G.

Further, once the route changing has been decided, it is possible toupdate a vehicle route to a new recommended route obtained by routere-searching. Therefore, it is possible to for the present invention toprovide a user with an excellent convenience by guiding the vehicleseamlessly even when the route is changed.

Particularly, since the navigation device 1 of the present embodimentpredicts a deviation of a vehicle from a recommended route (an omen ofroute changing) by detecting the behavior of the vehicle, it is notnecessary to determine whether the vehicle is traveling on a particularroad having a lane changing path adopted in prior art. Hence, thevehicle can be smoothly guided by starting a route re-searching at anearlier time without depending on the shape of road.

Also, since the navigation device 1 of the present embodiment starts aroute re-searching after limiting other routes to only one at step ST12of the flow chart shown in FIG. 3, it becomes possible to handle a routechange of a vehicle without increasing the processing load of therecommended route searching unit 8 formed by CPU or DSP.

However, at step ST10 or ST20, when several other routes are searched,several routes do not have to be limited to only one. At step ST13, theroute re-searching may be started among several other routes. At stepST14, when the route changing has been decided, the new recommendedroute going through the decided other route may be updated and displayedat step ST15 as the most recommendable route.

In this way, when the route re-searching is started among several otherroutes without processing at step ST12, during a searching process atstep ST10 or step ST20, routes are limited to those in the object anglerange WD1 or WD2. Therefore, even if the recommended route searchingunit 8 has a larger processing loader than an example of limiting otherroutes to only one, there will no considerably large load increase. Forthis reason, it is not necessary to limit other routes to only one.

Further, it is also possible to find other routes without limiting themto only one, exclude approach-forbidden roads such as one-way road fromthe searched other routes, and re-search a new recommended route basedon the remaining other routes.

Moreover, at steps ST11, ST21 and ST12, when it is impossible to limitother routes to only one, it is allowed to perform a route re-searchingby virtue of step ST30 without starting the route re-searching at stepST13.

For example, as shown in FIG. 5( a), when the recommended exit routesB1, B2 and B3 are at sharp curves and almost parallel to other route(1), and when the vehicle has turned to the directions of therecommended exit routes B1, B2 and B3, there is a possibility that therecommended exit routes B1, B2 and B3 can not be distinguished fromother route (1). For this reason, it is allowed to perform a routere-searching by virtue of step ST30 without starting the routere-searching at step ST13.

Whether the recommended exit routes B1, B2 and B3 are sharp curves canbe determined by comparing angles θ1 and θ2 as shown in FIG. 5( h). θ1is an angle formed between the direction θa of the recommendedapproaching route of a traveling vehicle and the recommended exit routeB1. θ2 is an angle formed between the recommended exit routes B1 and B2.When the angle θ2 is larger than the angle θ1, a curve at this time isdetermined to be a sharp curve.

As shown in FIG. 5( b), when the recommended exit route B issubstantially parallel to the other route (1), and when the vehicle hasturned to the direction of the recommended exit route B, there is apossibility that the recommended exit route B and other route (1) cannotbe distinguished from each other. For this reason, it is allowed toperform a route re-searching by virtue of step ST30 without starting theroute re-searching at step ST13.

As shown in FIG. 5( c), when, in addition to the recommended exit routeB, there are other routes (1) and (2) which are substantially parallelto each other, and when the vehicle has turned to the direction of otherroute (1) or other route (2), there is a possibility that other routes(1) and (2) cannot be distinguished from each other. For this reason, itis allowed to perform a route re-searching by virtue of step ST30without starting the route re-searching at step ST13.

As shown in FIG. 5( d), when, in addition to the recommended exit routeB, there are other routes (1) and (2) which are substantially parallelto each other, and when the vehicle has turned to the direction of therecommended exit route B, there is a possibility that other routes (1)and (2) cannot be distinguished from each other. For this reason, it isallowed to perform a route re-searching by virtue of step ST30 withoutstarting the route re-searching at step ST13.

As shown in FIG. 5( e), when the recommended exit routes B (i.e., B1,B2, B3 . . . ) are substantially parallel to other route (1), and whenthe vehicle has turned to the direction of other route (2) which is notparallel to other route (1), it is possible to find other route (1)excluding the recommended exit routes B (i.e., B1, B2, B3 . . . ),thereby starting the route re-searching at step ST13.

As shown in FIG. 5( f), when there is other route (1) substantiallyparallel to the recommended exit route B, and when the vehicle hasturned to the direction opposite to the recommended exit route B, it ispossible to find other route (2), thereby starting the routere-searching at step ST13.

In this way, when it is inevitably impossible to find other route, it ispossible to avoid a complex processing by not starting a routere-searching at step ST13, thereby obtaining an effect of reducing theprocessing load of CPU or DSP.

First Embodiment

A first embodiment will be explained with reference to FIGS. 6 and 7. InFIG. 6 the same signs are used to refer to the same or correspondingsteps in FIG. 3. Also, FIGS. 7( a) and (b) correspond to FIGS. 4( a) and(b) respectively, using same signs to represent the same orcorresponding parts.

Since the navigation device of the present embodiment is essentially thesame as the structure shown in FIG. 2( a), the explanation thereof isomitted here. However, description will be given to explain functions,operations and route re-searching function of the navigation device ofthe present embodiment.

The navigation device of the present embodiment performs substantiallythe same processing as shown in the flow chart of FIG. 3. However, asshown in the flow chart of FIG. 6, the processing at steps ST3A, ST4Aand ST5A are different from one another.

As shown in FIG. 6, data of the recommended route searched by therecommended route searching unit 8, data of the turning angle θxconstantly detected by the vehicle position determination unit 2, anddata of the vehicle position Px generated by the map matching unit 7 areinput into the route change determination unit 9. Then, at step ST1 theroute change determination unit 9 determines whether the vehicle isapproaching the branching point G by comparing the vehicle position Pxwith the recommended route (refer to FIGS. 7( a) and (b)).

When the route change determination unit 9 determines that the vehiclehas approached the branching point G, the process proceeds to step ST2,thus detecting the direction θa of the recommended approaching route Aand the direction θb of the recommended exit route based on respectivelinks.

Next, at step ST3A, the route change determination unit 9 sets, as thefirst angle range W1 and the second angle range W2, an angle rangedeveloping from the direction (θa+θth) to 180°, with the direction(θa+θth) being formed by adding a threshold θth to a reference directionθa.

In FIG. 7( a), the first angle range W1 is set to cover an angle rangedeveloping clockwise (rightward) from the right direction (θa+θth) tothe direction θr (180°), including the direction θb of the recommendedexit route B turning right with respect to the direction θa of therecommended approaching route A. The second angle range W2 is set tocover an angle range developing counterclockwise (leftward) from theleft direction (θa+θth) to the direction θr (180°). In FIG. 7( b), thefirst angle range W1 is set to cover an angle range developingcounterclockwise (leftward) from the left direction (θa+θth) to thedirection θr, including the direction θb of the recommended exit route Bturning left with respect to the direction θa of the recommendedapproaching route A. The second angle range W2 is set to cover an anglerange developing clockwise (rightward) from the right direction (θa+θth)to the direction θr.

Next, at step ST4A, the route change determination unit 9 determineswhether the turning angle θx of the vehicle is within the first anglerange W1 or not. Namely, at step ST4A, it is determined whether thevehicle has turned to the direction of the recommended exit route B andwhether the turning angle θx is the direction θxb within the first anglerange W1. Then, when the turning angle θx is determined to be within thefirst angle range W1 (“Yes”), the process proceeds to step ST10, and itis determined that the vehicle might change its route. On the otherhand, if the turning angle θx is not within the first angle range W1(“No”), the process proceeds to step ST5A.

At step ST5A, the route change determination unit 9 determines whetherthe vehicle turning angle θx is within the second angle range W2. Then,as shown in FIGS. 7( a) and (b), if the turning angle θx is determinedto be the direction θxa, and the θxa is determined to be within thesecond angle range W2, the process proceeds to step ST20 where it isdetermined that the vehicle might change its route. On the other hand,if the turning angle θx is determined to be out of the second anglerange W2 (“No”), the process proceeds to step ST6.

At step ST6, the route change determination unit 9 compares the vehicleposition Px with the coordinate of the node of the branching point G anddetermines whether the vehicle has passed through the branching point G.If the vehicle is determined to have passed through the branching point(“Yes”), the process proceeds to step ST30. If not (“No”), the processreturns back to step ST4A to repeat the previous steps.

Next, description will be given to explain an operation where the routechange determination unit 9 determines at step ST10 that the vehiclemight change its route. First, at step ST10, the route changedetermination unit 9 provides the recommended route searching unit 8with the result of the route change determination. Then, at step ST11,the object angle range WD1 is set to cover an angle range developingfrom the present turning angle θx to the direction θr in the range ofthe first angle range W1. Further, other routes (excluding therecommended exit route B) in the object angle range WD1 are searchedfrom the road data stored in the storage unit, and the process proceedsto step ST12.

At step ST12, the route change determination unit 9 determines whetherthe above-mentioned other route are only one. If it is determined thatthere is only one other route (“Yes”), the process proceeds to stepST13. If there are several other routes or there is no other route “No”,the process proceeds to step ST30.

Namely, as shown in FIGS. 7( a) and (b), if the vehicle turns to theright or left of the direction θa of the recommended approaching route Aand as a result there is only on other route R1 or L1 in the objectangle range WD1, the process proceeds to step ST13.

Next, at step ST13, the recommended route searching unit 8 starts theroute re-searching to find a new recommended route to guide the vehicleto the destination through the above-mentioned single one other route.Namely, in FIG. 7( a), the route researching is started to find a newrecommended route going through the single one other route R1. In FIG.7( b), the route researching is started to find a new recommended routegoing through the single one other route L1.

Next, at step ST14, the control unit 6 compares the vehicle position Pxwith the node of the branching point G to determine whether the vehiclehas passed through the branching point G and the route changing has beendecided. If it is determined that the route changing has been decided,the process proceeds to step ST15 to cause the display unit 4 to updateand display the new recommended route re-searched by the recommendedroute searching unit 8. Then, the process returns back to step ST1 torepeat the previous steps.

Next, description will be given to explain an example in which the routechange determination unit 9 has determined at step ST20 that the vehiclemight change its route. At first, the route change determination unit 9at step 20 provides the recommended route searching unit 8 with theresult of the route change determination. Next, at the step ST21, anobject angle range WD2 is set to cover an angle range developing fromthe present turning angle θx to the direction θr in the second anglerange W2. Then, other routes in the object angle range WD2 are searchedin the road data stored in the storage unit 3.

At step ST12, it is investigated whether there is only one other route.If yes (determined to be “Yes”), the process proceeds to step ST13. Ifthere are several other routes or there is no other route, it isdetermined to be “No” and the process proceeds to step ST30.

Then, at step ST13, the recommended route searching unit 8 starts theroute searching to find a new recommended route to guide the vehicle tothe destination through the above-mentioned single other route, based onthe route change determination result fed from the route changedetermination unit 9. Subsequently, at step ST14, the control unit 6determines whether the vehicle has passed through the branching point Gand route changing has been decided. If it is determined that the routechanging has been decided, the process proceeds to step ST15 to causethe display unit 4 to update and display the new recommended routere-searched by the recommended route searching unit 8. Afterwards, theprocess returns back to step ST1 to repeat the previous steps.

As discussed above, when the route change determination unit 9determines at the step ST6 that the vehicle has passed through thebranching point G, the process proceeds to step ST30. If it isdetermined at step ST12 that other route is not only one, the processproceeds to step ST30. At this time, the control unit 6 determineswhether the vehicle has passed through the branching point G and theroute changing has been decided. If it is determined at step ST30 thatthe route changing has been decided, the recommended route searchingunit 8 is caused to perform the route re-searching. Namely, what isexecuted at step ST30 is not to predict an omen of vehicle routechanging so as to perform a route re-searching, but to re-search a newrecommended route going through other route at the time the routechanging has been decided. Subsequently, the process proceeds to stepST15 to cause the display unit 4 to update and display the newrecommended route. Then, the process returns back to step ST1 to repeatthe previous steps.

As explained above, according to the navigation device of the presentembodiment, when the vehicle enters the branching area of the branchingpoint G, a direction θr is set to 180° opposite to the direction θa ofthe recommended approaching route A. Meanwhile, the first angle range W1is set to cover an angle range developing from the direction (θa+θth) tothe direction θr including the direction θb of the recommended exitroute B; the second angle range W2 is set to cover an angle rangedeveloping from the direction (θa+θth) to the direction θr excluding thedirection θb of the recommended exit route B. When a turning angle θx iswithin the first angle range W1 or the second angle range W2, it isdetermined that there is a deviation from the recommended route (an omenof route changing) and a route re-searching is started, therebyrendering it possible to start an earlier route re-searching before thevehicle passes through the branching point G.

Namely, when it is detected that the vehicle turning angle θx is withinan angle range having the direction θa of the recommended approachingroute A as a reference and excluding an angle range of a threshold valueθth, and that the turning angle is an angle developing from thedirection θa of the recommended approaching route A and exceeding thedirection θb of the recommended exit route B, or an angle opposite tothe direction θb of the recommended exit route B, a route-researching isstarted, thereby rendering it possible to start a route re-searching atan earliest time.

Once the route changing is decided, it is possible to update an oldroute into a new recommended route re-searched. Therefore, the presentinvention can provide a user with an excellent convenience by ensuring aseamless guiding even when the route is changed.

Particularly, with the navigation device 1 of the present embodiment,since it is possible to detect the behavior of a vehicle and predicts adeviation (an omen of route changing) from the recommended route of thevehicle, it is not necessary to determine whether the vehicle istraveling on a special road having a lane changing path as equipped inprior art. Therefore, the navigation device can guide seamlessly bystarting the route re-searching early without depending on the shape ofa road or the like.

Further, with the navigation device of the present embodiment, at stepST12 of the flow chart shown in FIG. 6, since route re-searching isstarted after other routes are limited to only one, it is possible tohandle a vehicle route change without increasing a processing load ofthe recommended route searching unit 8 formed of the CPU or DSP.However, similar to the preferred embodiment, the navigation device ofthe present embodiment does not have to necessarily require that otherroutes be limited to only one. Further, it is also possible to searchother routes without limiting them to only one route, excludeapproach-forbidden road such as one-way road from the searched otherroutes, thereby re-searching a new recommended route based on theremaining other routes.

Second Embodiment

Next, a second embodiment will be explained with reference to FIGS. 8through 10. FIG. 8( a) is a bock diagram showing the constitution of thenavigation device 1 of the present embodiment. FIGS. 8( b) through (e)are views briefly explaining the functions of the navigation device 1.FIG. 9 is a flow chart showing the functions and operations of thenavigation device 1. FIG. 10 is a graph explaining the functions of thenavigation device 1. In FIGS. 8 and 9, portions which are the same as orcorresponding to those in FIGS. 2 through 7 are represented by the samereference numerals.

As shown in FIG. 8( a), the navigation device 1 of this embodiment hasthe same constitution as the above-mentioned preferred embodiment or thefirst embodiment (refer to FIG. 2( a)), including the vehicle positiondetection unit 2, storage unit 3, display unit 4, operation unit 5,control unit 6, map matching unit 7, recommended route searching unit 8,and route change determination unit 9A.

The vehicle position detection unit 2, storage unit 3, display unit 4,operation unit 5, control unit 6, map matching process unit 7, andrecommended route searching unit 8, have the same functions as thepreferred embodiment or the first embodiment. However, the route changedetermination unit 9A predicts the route change of the vehicle by havingdifferent functions from the route change determination unit 9 shown inFIG. 2( a).

Next, description will be given to mainly explain the route changedetermination unit 9A serving as the featured portion of thisembodiment.

At first, description will be given to explain the function of the routechange determination unit 9A.

In the navigation devices of the preferred embodiment and the firstembodiment, the route change determination unit 9 predicts a deviationof a vehicle from a recommended route (an omen of route changing of thevehicle) based on a turning angle of the vehicle entering the branchingarea of a branching point.

On the other hand, the route change determination unit 9A of the presentembodiment determines a deviation of the vehicle from a recommendedroute (an omen of route changing) based on a relationship among arecommended approaching route and a recommended exit route bothconnected to the branching point, the speed of a vehicle entering thebranching point, and a distance from the vehicle position to thebranching point.

For example, when the direction of the recommended approaching route Aand the direction of the recommended exit route B both connected to thebranching point G are substantially equal to each other as shown in FIG.8( b), when the recommended routes B1, B2, and B3 are curves withrespect to the recommended approaching route A connected to thebranching point G as shown in FIG. 8( c), and when the recommended exitroute B is a right or left turning route with respect to the recommendedapproaching route A connected to the branching point G as shown in FIGS.8( d) and (e), it is determined whether the vehicle approaching thebranching point G is going to change its route based on the relationsamong the recommended approaching route, the recommended exit route, thevelocity of the vehicle approaching the branching point, and thedistance from the vehicle position to the branching point.

The functions of the navigation device 1 (mainly the functions of theroute change determination unit 9A) will be explained below withreference to a flow chart shown in FIG. 9. Further, reference will alsobe made to FIGS. 8( b) to (e) during the following description.

As shown in FIG. 9, the data of the recommended route searched by therecommended route searching unit 8, the data of the turning angle θxdetected constantly by the vehicle position detection unit 2, and thedata of the vehicle position Px generated by the map matching unit 7 areinput into the route change determination unit 9. Then, at the stepST100, the route change determination unit 9 compares the vehicleposition Px with the recommended route and determines whether thevehicle has approached the branching point G. When the vehicle positionPx is within a specified distance from the branching point G, thevehicle is determined to be approaching the branching point G.

When the route change determination unit 9 determines that the vehiclehas approached the branching point G, the process proceeds to stepST200, thereby detecting the direction θa of the recommended approachingroute A and the direction θb of the recommended exit route bothconnected to the branching point G, based on the respective links.

At step ST300, the route determination unit 9, taking the direction θbas a reference (0°), compares a specified threshold angle Δθ to avariation angle (θa−θb) which is a direction θa with respect to thedirection θb and determines whether the variation angle (θa−θb) islarger than the threshold angle Δθ. Here, the threshold angle Δθ is setto avoid a possibility that the direction of the recommended exit routeθb is small with respect to the direction θa of the recommendedapproaching route. When the directions of the recommended approachingroute A and the recommended exit route B are substantially equal to eachother as shown in FIG. 8( b) and when the recommended exit routes B1,B2, and B3 are gentle curves with respect to the recommended approachingroute A as shown in FIG. 8( c), the threshold angle Δθ is set beforehandto determine that the above-mentioned variation angle (θa−θb) is smallerthan the threshold angle Δθ.

In particular, for example, by setting the threshold angle Δθ at about45°, when the variation angle (θa−θb) is smaller than the thresholdangle Δθ, it is possible to determine that the recommended exit route Bis substantially the same or only gently curved with respect to therecommended approaching route A.

Then, at step ST300, when it is determined that the variation angle(θa−θb) has exceeded the threshold angle Δθ (“Yes”), the processproceeds to step ST400. When it is determined that the angle (θa−θb) isnot larger than the threshold angle Δθ (“No”), the process returns backto step ST100 and starts all over again.

Next, at step ST400, the route change determination unit 9 finds, fromthe distance conversion data stored in the storage unit 3, a distance DSrequired to travel to the recommended exit route through the branchingpoint G (thereafter, referred to as “required distance”), based on thevehicle speed Vx provided by the vehicle position detection unit 2.

As shown in FIGS. 8( e) and (f), when the recommended exit route Bconnected to the branching point G is a route to turn to the right orleft of the recommended approaching route A, a higher speed of thevehicle traveling on the recommended approaching route A will cause alonger necessary distance DS from the vehicle position Px to thebranching point G, because of a necessity to reduce the vehicle speed orthe like.

Then, the distance conversion data indicating a relationship (shown inFIG. 10) between the vehicle speed and the required distance for thevehicle to turn right or left, is searched from the storage unit 5 basedon the vehicle speed Vx, thereby obtaining the distance DS required forthe vehicle speed Vx.

FIG. 10 shows an example in which the recommended exit route B turnsabout 90° to the right or left of the recommended approaching route A.The storage unit 3 also stores the distance conversion data indicating adistance required to turn right or left other than 90° with respect tothe vehicle speed Vx. When the angle of the recommended exit route Bwith respect to the recommended approaching route A is other than 90°,searching is performed to find the distance conversion data notinvolving 90°, thereby obtaining the distance DS required for thevehicle speed Vx.

Next, at step ST500, the route change determination unit 9 calculates anactual distance DSR from the vehicle position Px to the branching pointG, based on the vehicle position Px provided by the map matching unit 7and the node data (coordinate information) of the branching point G.Then, the route change determination unit 9 compares the actual distanceDSR with the above-mentioned required distance DS, thereby determiningwhether the distance DSR is shorter than the required distance DS. Ifthe actual distance DSR is shorter than the required distance DS, theprocess proceeds to step ST700. On the other hand, if the actualdistance DSR is longer than the required distance DS, the processproceeds to step ST600 and then returns back to step ST400 to repeat theprevious steps until the vehicle passes through the branching point G.

Namely, the route change determination unit 9 determines at step ST500whether the actual distance DSR is shorter than the required distanceDS, thereby performing an equivalent process equal to a process ofdetermining whether the vehicle is traveling at a speed not able to turnright or left at the branching point G.

Next, at step ST700, the route change determination unit 9 searches theroad data stored in the storage unit 3 for other route connected to thebranching point G, excluding the recommended exit route B and the routeson which the vehicle cannot turn right or left when traveling at thevehicle speed Vx. Then, the process proceeds to step ST800.

At step ST800, the route change determination unit 9 investigateswhether the searched other routes are only one. If other routes are onlyone (“Yes”), the process proceeds to step ST900. If other routes areseveral or none “No”, the process proceeds to step ST1000.

Next, at step ST900, the recommended route searching unit 8 starts theroute re-searching to find a new recommended route to guide the vehicleto the destination through the above-mentioned single other route.Further, the control unit 6 compares the vehicle position Px to the nodeof the branching point G and determines whether the vehicle has passedthrough the branching point G and the route changing has been decided.If it is determined that the route changing has been decided, thedisplay unit 4 will be caused to update and display the new recommendedroute searched by the recommended route searching unit 8. Subsequently,the process returns back to step ST100 again to repeat the previoussteps.

Next, once the process shifts from the above-mentioned step ST600 orstep ST800 to step ST1000, the control unit 6 determines at step ST1000whether the vehicle has passed through the branching point G and theroute changing has been decided. If the route changing has been decided,the recommended route searching unit 8 is caused to start a routere-searching. Namely, what is required is not of predicting a vehicleroute deviation from a recommended route (an omen of route changing) andthen performing a route re-searching, but re-searching a new recommendedroute going through other route at the time the route changing isdecided. Then, the new recommended route is updated and displayed in thedisplay unit 4, and the process returns back to step ST100 again torepeat the previous steps.

As described above, according to the navigation device 1 of the presentembodiment, an actual distance DSR from the vehicle position Px to thebranching point G is compared to a required distance DC up to thebranching point G which is necessary for the vehicle to travel throughthe recommended exit route B on which the vehicle enters the branchingpoint G from the recommended approaching route A and turns right or leftat the speed Vx. If the actual distance DSR is shorter than the requireddistance DS, it is determined that the vehicle will not travel throughthe recommended route B on which the vehicle turns right or left,thereby rendering it possible to start a route re-searching at anearliest time.

If an actual distance DSR is shorter than the required distance DS, itis determined that the vehicle will change its route to other routewhich allow it to travel at the present speed Vx (for example, astraight route C shown in FIGS. 8( e) and (f)) or other route on whichthe vehicle can travel along a gentle curve, thereby making it possibleto start a route re-searching at an earliest time based on those otherroutes.

1. A navigation device formed such that when guiding a vehicle by virtue of a recommended approaching route and a recommended exit route both connected to a branching point, and once the vehicle traveling from the recommended approaching route and heading for the branching point is about to deviate from the recommended exit route, said navigation device starts a route re-searching for finding a new recommended route going through other route, wherein said navigation device comprises route change determination device for detecting that a turning angle of the vehicle is about to be in a direction within an angle range not including an angle formed between the direction of the recommended approaching route and the direction of the recommended exit route, thereby starting the route re-searching.
 2. A navigation device formed such that when guiding a vehicle by virtue of a recommended approaching route and a recommended exit route both connected to a branching point, and once the vehicle traveling from the recommended approaching route and heading for the branching point is about to deviate from the recommended exit route, said navigation device starts a route re-searching for finding a new recommended route going through other route, wherein said navigation device comprises route change determination device for detecting that a turning angle of the vehicle is within an angle range not including a predetermined threshold angle range having the direction of the recommended approaching route as a reference, is about to be in a direction exceeding a direction of the recommended exit route from a direction of the recommended approaching route, or a direction opposite to the direction of the recommended exit route, thereby starting the route re-searching.
 3. The navigation device according to claim 1 or claim 2, wherein the route change determination device detects another route existing in an angle range developing from a turning angle of the vehicle to an angle of 180° opposite to the direction of the recommended approaching route, and starts the route re-searching to find a new recommended route going through said another route.
 4. The navigation device according to the claim 3, wherein the route change determination device starts the route re-searching when the detected other route is only one.
 5. (canceled)
 6. (canceled)
 7. (canceled)
 8. A navigation method constituted such that when guiding a vehicle by virtue of a recommended approaching route and a recommended exit route both connected to a branching point, and once the vehicle traveling from the recommended approaching route and heading for the branching point is about to deviate from the recommended exit route, said navigation method starts a route re-searching for finding a new recommended route going through other route, wherein said navigation method comprises a route change determination step for detecting that a turning angle of the vehicle is about to be in a direction within an angle range not including an angle formed between the direction of the recommended approaching route and the direction of the recommended exit route, thereby starting the route re-searching.
 9. A navigation method constituted such that when guiding a vehicle by virtue of a recommended approaching route and a recommended exit route both connected to a branching point, and once the vehicle traveling from the recommended approaching route and heading for the branching point is about to deviate from the recommended exit route, said navigation method starts a route re-searching for finding a new recommended route going through other route, wherein said navigation method comprises a route change determination step for detecting that a turning angle of the vehicle is within an angle range not including a predetermined threshold angle range having the direction of the recommended approaching route as a reference, is about to be in a direction exceeding a direction of the recommended exit route from a direction of the recommended approaching route, or a direction opposite to the direction of the recommended exit route, thereby starting the route re-searching.
 10. (canceled) 